Example of <Validation> Statement

Validation expressions allow you to specify logic to determine whether a value entered in a form is valid.

The validation expression returns null to indicate success, or a string containing a readable error message to indicate failure. The system displays the validation error message in red text at the top of the form.

The following example contains the logic to determine whether the age entered by user in a field is greater than 0. This expression returns null if the age is greater than or equal to zero.

<Field name=’age’>
   <Validation>
     <cond>
       <lt>
         <ref>age</ref>
         <i>0</i>
       </lt>
       <s>Age may not be less than zero.</s>
     </cond>
   </Validation>
</Field>